The purpose of this four-year two-city study, entitled "AIDS Risk in Older Urban Adult Senior Housing Residents," is to identify high-risk drug and sexual exchanges associated with HIV transmission among lower income older adults and other residents of diverse ethnic backgrounds living in older adult housing in the cities of Hartford and Chicago -- both regional epicenters with very high rates of HIV. Aims are: (1) to use ethnography to identify risky exchanges in target high-risk buildings in both cities; (2) to use ethnographic, epidemiologic and network research methods to identify individual and social structural factors associated with drug- and sex-risk behaviors among older adult buildings residents (N=1600, 800 in each city); (3) to determine HIV prevalence among building residents; and (4) to use resulting data to develop and assess for feasibility and acceptability intervention strategies for use in high risk buildings in study cities and elsewhere. The study will be conducted in three stages. Stage 1 will involve pilot ethnography in two buildings in each city to identify risky exchanges, pilot test epidemiologic and network instruments, develop a building risk index, and identify and assign buildings to the study sample. Stage 2 will consist of ethnography, epidemiologic and network surveying in 6 buildings in each city, conducted in six waves consisting of approximately 4 months each. Stage 3 will involve: data analysis; formulation of intervention approaches appropriate to building-level social structures, and identified individual and environmental risk factors in both cities; dissemination of data; and evaluation of feasibility and acceptability of proposed intervention approaches in buildings and agencies in both locations.